Deflection device for a color television display tube

ABSTRACT

A deflection device for a color television display tube having three electron beams which extend in one plane, comprising two pairs of ferromagnetic control members which are diametrically arranged and which are rotatable about the tube neck, and which serve for the adjustment of the quantity of magnetic flux applied from the stray field of the deflection coils to the electron beams.

United States Patent 1191 Paridaens Oct. 14, 1975 [54] DEFLECIION DEVICE FOR A COLOR 3,553,523 l/197l Budd 313/412 X D TUBE 3,701,065 10/1972 Mirsch..... TELEVISION ISPLAY 3,725,831 4/ 1973 Barbin 335/212 [75] Inventor: Cornelis Johannes Henricus 'Paridaens, Eindhoven, Netherlands Prima Examiner-G. Harris 73 A U.S. Phl C rat n New ry Sslgnee I lps orpo l0 Attorney, Agent, or Firm-Frank R. Trifari; George B.

York, NY.

Berka [22] Filed: Oct. 1, 1974 [21] Appl. No.: 511,048

- [57] ABSTRACT [30] Foreign Application Priority Data Oct. 10, 1973 Netherlands 7313905 A deflection device for a color television display tube having three electron beams which extend in one [52] U.S. Cl. 335/212; 335/210 plane, comprising two pairs of ferromagnetic control [51] Int. Cl. HOlF 1/00 members which are diametrically arranged and which [58] Field of Search 335/210, 212; 313/412, are rotatable about the tube neck, and which serve for 313/421, 425, 426, 427, 428 the adjustment of the quantity of magnetic flux applied from the stray field of the deflection coils to the [56] References Cited electron beams.

UNITED STATES PATENTS 2,730,642 1/1956 Grosjean 335 212 x 2 Claims, 3 Drawing Figures DEFLECTION DEVICE FOR A COLOR TELEVISION DISPLAY TUBE The invention relates to a deflection device for a color television display tube, comprising a device for generating three electron beams which are situated in substantially one plane and two parallel ferromagnetic correction plates, arranged between the central beam path on the one side and each of the outer beam paths on the other side,'the edges of the plates parallel to the beam paths being bent outwards (see, for example, British Patent Specification No. 1,210,341). The correction plates intercept, as will yet be described, part of the stray field of the vertical deflection coils and conduct this part to the central electron beam, with the result that the vertical deflection thereof is intensified at the expense of that of the two outer beams. A convergence error which frequently occurs in a display tube comprising three beams arranged in one plane is thus substantially corrected. Complete correction, however, is possible only if the degree of correction can be controlled; the invention has for its object to provide an inexpensive facility for such control.

The invention is characterized in that the neck of the display tube is enveloped, approximately at the area of the correction plates, by two pairs of soft-ferromagnetic control members which are diametrically arranged with respect to the tube neck and which extend along the circumference of the tube neck at angles of less than 90, the said pairs being rotatable about the tube neck.

The invention will be described in detail hereinafter with reference to a drawing.

FIGS. 1 and 2 are a side elevation and a crosssectional view, respectively, of an embodiment according to the invention, and

FIG. 3 illustrates the device of FIGS. 1 and 2 in a different position of adjustment.

FIG. 1 shows a part of the neck 1 of a color television display tube comprising three electron beams arranged in one plane, the said beams being generated therein by means of three electron guns 3, 5 and 7 (see also FIG. 2). Arranged about the neck 1 is a deflection coil system of the usual construction, the said system comprising, for example, saddle-like horizontal deflection coils 9 and vertical deflection coils 13 which are toroidally wound about a ferromagnetic yoke ring 11.

A deflection error is found to occur in such display tubes because the central electron beam is deflected slightly less in the vertical direction than the two outer beams. So as to correct this error, inside the tube neck two substantially parallel ferromagnetic correction plates 15 and 17 are arranged between the central beam path on the one side and each of the two outer beam paths on the other side (the beam paths are considered to extend coaxially with respect to the associated electron guns). The correction plates are preferably arranged in the tube neck immediately behind the deflection coil system, and the edges of the plates which are parallel to the beam paths are bent outwards as is illustrated in FIG. 2.

As is shown, the vertical deflection field extends horizontally and substantially within the space between the deflection coils, but a small part-which can be referred to as stray field-extends outside the said space. In toroidal vertical deflection coils the principal part of the deflection field extends in the yoke 11 from the one side thereof to the other side, whilst the stray field extends mainly axially from the edges of the ring outwards, after which it is deflected 90. Following this change of direction, the stray field is parallel to the main field and the shape of the stray field on the rear of the yoke ring 11, as denoted by the arrows in FIG. 2, reveals that the plates 15 and 17 cause a field concentration at the area of the central electron beam, while the stray field through the plates is guided somewhat around the outer beam paths.

It will be obvious that the deflection of the central electron beam is thus slightly increased at the expense of that of the two outer beams, so that the said error is corrected. In order to control this correction, according to the invention the tube neck 1 has arranged thereabout, at the area of the correction plates 15 and 17, two pairs 19 and 21 of diametrically arranged soft-fen romagnetic control members, preferably in the form of identical arcs of a circle of less than 90 which are coaxial with respect to the tube neck, the said pairs being rotatable about the tube neck. In the embodiment shown in FIGS. 1 and 2, the control members are plates of mu-metal which are pair-wise separately connected to the facing sides of two non-magnetic annular discs 23 and 25 which are rotatable about the tube neck 1. To be specific, the pair of members 19 is connected to the disc 23, and the pair of members 21 is connected to the disc 25 (for example, by gluing).

The procedure to be followed is to adjust the position of the two pairs of members 19 and 21 between the two extreme positions shown in FIGS. 2 and 3, respectively, by turning the discs 23 and 25 in opposite directions. In the position shown in FIG. 2 the control members cause substantially no change-ignoring a small enlargement of the part of the stray field extending between and through the correction plates 15 and l7in the course of the stray field, which should be so large at the area of the central electron beam that an excessive correction (overcompensation) of the said error occurs. In the position shown in FIG. 3, however, the magnetic shunt effect of the control members attenuate the stray field at the area of the central electron beam such that the correction is too small. It will be obvious that always an intermediate position can be found in which optimum correction is achieved.

What is claimed is:

l. A deflection device for a color television display tube, which includes a device for generating three electron beams which are situated in substantially one plane and two parallel ferromagnetic correction plates, arranged between the central beam path on the one side and each of the outer two beam paths on the other side, the edges of the plates parallel to the beam paths being bent outwards, comprising two pairs of soft-ferromagnetic control members which are diametrically arranged with respect to the tube neck and which extend approximately at the area of the correction plates along the circumference of the tube neck at angles of less than the said pairs being rotable about the tube neck.

2. A device as claimed in claim 1, wherein the control members are flat plates in the form of identical arcs of a cricle of less than 90 which are coaxial with respect to the tube neck, the two pairs being separately connected to the two facing sides of two non-magnetic annular discs which are rotatable about the tube neck. 

1. A deflection device for a color television display tube, which includes a device for generating three electron beams which are situated in substantially one plane and two parallel ferromagnetic correction plates, arranged between the central beam path on the one side and each of the outer two beam paths on the other side, the edges of the plates parallel to the beam paths being bent outwards, comprising two pairs of softferromagnetic control members which are diametrically arranged with respect to the tube neck and which extend approximately at the area of the correction plates along the circumference of the tube neck at angles of less than 90*, the said pairs being rotable about the tube neck.
 2. A device as claimed in claim 1, wherein the control members are flat plates in the form of identical arcs of a cricle of less than 90* which are coaxial with respect to the tube neck, the two pairs being separately connected to the two facing sides of two non-magnetic annular discs which are rotatable about the tube neck. 